Posted
by
Soulskill
on Monday March 21, 2011 @07:30PM
from the can-we-make-them-levitate dept.

prunedude tips this quote from a post at Freakonomics about Japan's nuclear crisis:
"The folks over at IV Insights, the blog associated with Nathan Myhrvold's Intellectual Ventures, point out that it was the complete loss of power that disabled the cooling systems protecting the plant's reactors. Which raises the question: Is there nuclear technology that could withstand such a catastrophe? Possibly. TerraPower, an Intellectual Ventures spin-off that also boasts Bill Gates as an investor, is working on a new reactor design called a traveling wave reactor that uses fast reactor technology, rather than the light water technology used at the Fukushima Daiichi plant. The two biggest advantages of the fast reactor design is that it requires no spent fuel pools and uses cooling systems that require no power to function, meaning the loss of power from the tsunami might not have crippled a fast reactor plant so severely."

My understanding is that breeder reactors and pebble bed reactors wouldn't have had the problem that hit the plant in Japan. That and breeder reactors have the added benefit of eating nuclear waste over and over until whatever is left might make you sneeze. Maybe I'm completely off on that, but why do we need a new design on this kind of reactor unless it's relatively simple to retrofit older reactors?

Germany ran a pebble bed reactor at the Nuclear Research Facility at Juelich. The Juelich post-mortem report concluded that pebble bed reactors have severe problems in practice (at least some of them base design flaws), in the specific case of the Julich AVR reactor leading to Strontium-90 contamination of the soil and aquifer beneath the reactor.

The AVR primary circuit is heavily contaminated with metallic fission products (Sr-90, Cs-137) which create problems in current dismantling. The amount of this contamination is not exactly known, but the evaluation of fission product deposition experiments indicates that the end of life contamination reached several percent of a single core inventory, which is some orders of magnitude more than precalculated and far more than in large LWRs.[...]It leads to the conclusion that the AVR contamination was mainly caused by inadmissible high core temperatures, increasing fission product release rates, and not - as presumed in the past - by inadequate fuel quality only.

From the conclusions:

As outlined above there exist unresolved safety problems in pebble bed reactors for design basis accidents, as for beyond design basis accidents like severe air ingress with graphite burning. Previously a superior safety behaviour of pebble bed reactors was claimed compared to other nuclear systems including an allegedly catastrophe free design. According to the above presents arguments there are doubts, whether this depicts reality.

So while pebble bed reactors have some advantages over traditional designs, they are by no means the silver bullet that some people make them to be.

Most of those problems are about shielding and disposing of the plant when you shut it down. The remainder can be solved by using a moderator that doesn't burn. You don't have to use graphite. You could, for example, use beryllium....

A lot of the safety of the pebble bed design comes from the TRISO fuel particles that it uses. In the even of an accident like the one at Fukushima there would be no concern over the fuel melting down since the power density is so low and the melting point of graphite is so high there is no possible way for the fuel to melt down. These particles can be used in any sort of a Very High Temperature Gas Cooled Reactor, of which the gas cooled pebble bed and prismatic designs are both very attractive options.

The TRISO particle is mostly a lump of charcoal. With the pebble bed design, you can get one of two major issues:a. oxygen (i.e. outside air) incursion - obviously, results in a fireb. water (i.e. secondary coolant) incursion -results in at least a steam explosion, if not explosion+fire, if not even a (localized?) power excursion from the temperature drop and additional moderation.

One instance of that design is 20 miles from here. It is only a small reactor built to study this type of reactor. It has contaminated the soil and groundwater beneath it. It has been very close to exceeding the worst case scenario for this type of reactor and only luck prevented a catastrophe. It is unclear if the dismantling of the reactor is technically possible in the planned timeframe because the containment is much more radioactive than expected. Scientists working at the institute which operated the

It doesn't matter how safe they are, the forces of extreme environmentalists and Luddites will say No! No! No!

Already idiots in Congress, without knowing anything more than the hyperbolic news reports, are calling for shut downs and "slow downs" and endless Congressional Investigations where people who know about Nuclear Power try to convince people that don't that you can't burn a hole in the earth straight through to China

I'm eternally optimistic that our fine congressfolk know better. Most of 'em, anyway. And that they are calling for shutdowns and slow downs as a response to their constituents - because they are spineless and because nobody [at the top] has stood up and said "we can and should make better, safer reactors."

I've always loved that... for starters what's most likely to happen is the molten goo hits the water table resulting in a flash boil the blows toxic, radioactive crap everywhere. The less likely possiblity (and this is WAY remote) is that it burns burns all the way through the mantle and becomes lava. (then you have lava and toxic, radioactive crap everywhere.:-))

Can a pebble bed reactor survive: The complete & total loss of any supporting structures which keep the fuel pebbles at a distance, the simultaneous loss of its cooling system, and the complete loss of *every single control system in place*? Plus the complete failure of humans not to do *exactly the wrong thing in every single instance in a crisis*? Or to not be able to do anything at all? (Say chemical weapon attack?) Not hours, not days, not weeks, indefinitely -- without being a risk to those living

That's not exactly surprising. A lot of claims that nuclear reactors are "safe" have turned out to be lies, and the nuclear industry seems to have a long history of cover-ups (including several cover-ups of major safety violations at the Fukushima Daiichi plant). It would appear that pebble bed reactors fall into that category [slashdot.org].

The extreme environmentalists only have a problem with the waste disposal - the fact that it takes 10,000 years or more for it become safe. If these new reactors will actually use nuclear fuel until it's about as radioactive as any other natural source, the "extreme" environmentalists will be behind it 100%.

No they won't. Even if the radioactive materials are rendered into lead, they'll complain that:

It is poisonous!

Its elemental symbol is Pb, which is also short for peanutbutter, which causes deathly allergies in children

The *Extreme* environmentalists will also complain that:

Uranium was mined from mother Gaea, hurting her

Any energy production helps support an unnatural amount of humans who will continue to rape mother Gaea

Me: vegan, no car, mid-40's, computer geek, Buddhist, atheist, totally love nuke power, still hoping for better but realistic. Seriously, why assume the lowest common denominator has any bearing on what will actually happen? Or are you trying to demonstrate that straw men make better fuel?

For example. Amory Lovins, one of the notables of the anti-nuclear movement was asked in an interview what he thought of a truly cheap clean energy source. He said it would be a disaster. Why? Because he believes that whenever humans are given concentrated sources of power, they use it to destroy nature. Thus humans need to be limited to diffuse and limited sources of energy.

Quite often the waste and radiation questions are arguments used against nuclear power, when some of the motivation would have problems with any concentrated source of energy.

Needless to say, I disagree with that viewpoint, but it is one that can be argued and is not totally without merit.

All they needed was a backup supply of water that would be gravity-fed. One big tank on that big hill behind the plant, with a nice, flexible hose leading to a fat, manual valve behind enough shielding to protect someone even if the reactor was breached.

(Pardon my English Engineering units)Let's see, 2.3 feet per psi, 1000 psi steam pressure (According to wikipedia, sounds a bit high to me) so we are looking at a 2300 foot high hill. If it's 600 psi steam, at least after shutdown, then it's only about 1700 feet of hill.

And the big tank has to still be there after the 9.0 earthquake. There is more complication in "All they needed" than you think.

The basic design is supposed to have a steam powered feed pump with a source of makeup water. Whether it broke, was never there, or the source of makeup water was a condenser that was mudded out by the tsunami, I don't know. And I would like to know. I used to serve on an SSN, so I have a certain professional curiosity.

The premise "that it was the complete loss of power that disabled the cooling systems protecting the plant's reactors"
in the original post is incorrect.
Causes for failures on the JA plants were many.
Besides being under-designed for a 9 earthquake (7.? designed) and a too low tsunami wall to hold up the one occurred, there were failures in maintenance/upkeep/supervision.

Any plant can have those "failures" and the "uups, we did not think of that ever happening" is too costly and will happ

It can't believe nobody has mentioned this, but the reactor designs were not the problem. All of these cooling problems could have been solved by some sort of waterproof backup power, even if it had to be stored 50 miles away and delivered via an underground cable that comes up under the reactors. Some of these reactors' cooling systems failed because the battery backup power was in the farking basement for crissakes! Below sea level on an Island! Totally flooded. I'm a social science (excuse the contradiction of terms) and I know better than that.

How hard would it be to either 1) keep battery backup at a high point above a nuke plant* (I know, weight, whatever, engineer around it) or 2) the plan I mentioned above, the same redundancy that data centers have, redundant power located elsewhere. Either would have likely saved these reactors.

So it's a building designed to withstand an earthquake larger than any that has been recorded in history. It's a building with a 6m tsunami wall around the grounds to withstand a larger tsunami than has ever been experienced anywhere on that pacific rim. Oh and it had battery backup that is stored in a sealed room which was completely unaffected by all the above and worked entirely as intended, but ultimately ran out of juice.

Basic planning. You don't rely on your backup backup to run the plant as it's designed. You rely on that first backup in case the main system fails, and you rely on the second backup to buy you enough time to restore one of the primary backups. This is common in all industrial situations. Here's a question for you, can your datacentre run indefinitely on battery power, or does battery power only keep you up for an hour or so to ensure that your diesel generators have a) time to kick in, and b) if they are out you can reasonably expect main power to come on within the intended time anyway?

Here's another question for you. Has your disaster plan taken into account a direct nuclear strike? I mean just because it hasn't happened before doesn't mean it couldn't happen right? What about an alien attack? Both of these were just as likely to occur as an earthquake of this magnitude followed by a tsunami of that size.

While you may have a point, that hardly works as an argument against such reactors being built in France, say, or China (both of whom have nuclear bombs, and plenty of nuclear reactors of various designs).

I doubt many people would say that the US can't build a type of reactor for fear of it allowing them to get nuclear bombs...

Did you even bother to look at the travelling wave reactor info? Did you just hear the word "fast" or breeder and stop?

It's designed to make proliferation nearly impossible. That's a big reason why Gates is interested.

It only generates the fissile fuel in a narrow strip where the reaction is going on, and then burns it up. In front of the reaction wave, no plutonium. Behind the wave, maybe some traces left. In the wave, it's an active reaction. That's a touch difficult to turn into a bomb.

The thing is, even prior to this disaster we had designs that would have safeguarded against it (Pebble Bed Reactors aren't new). It just cost too much to tear down the old ones and build nice safe ones. Well, now we have a nice, big example to point to of why fiscal conservativeness is not always the most effective long-term strategy.

See above for the comments on Pebble Beds. It appears that even after decades of research and engineering into nuclear reactors, we still don't know enough to be confident that any particular design or implementation will behave the way the designers expect. Not exactly surprising since anything more complicated than a paper towel seems to have those same issues but it does mean that any progress will have to come slowly and hopefully carefully.

Just because it looks good in Autocad doesn't mean it will actually work correctly.

Supposedly the pebble-bed reactor type is also resistant to the type of damage suffered at the Fukushima plants, and it has the added bonus of not being encumbered by ex-Microsoft patent trolls. I remember reading that the Germans had been experimenting with the design but dropped it for political reasons.

Actually, the pebble reactor in Julich, Germany (I'll assume that's what you are referring to) had severe problems leading to long half-life fission products contaminating the soil and water around the reactor.

It's not ignored. CANDU reactors can use Thorium. That means, for example, all of Ontario, Canada's reactors (which provide more than 50% of Ontario's power mix) could switch to Thorium without problems.

Wikipedia "Candu". The article runs down all the special features. It's the multi-fuel stove of reactors, able to burn other reactor's waste, old nuclear weapons. The last comment, after enthusing about that, is that it can "breed fuel from thorium". So it's an extra step, and thorium isn't cheap enough (or uranium is) to make it worthwhile.

Still, it's bonus that they're proof against the year of Peak Uranium.

Some of the benefits of thorium when compared with uranium as fuel:
* Weapons-grade fissionable material (U-233) is harder to retrieve safely and clandestinely from a thorium reactor;
* Thorium produces 10 to 10,000 times less long-lived radioactive waste;
* Thorium comes out of the ground as a 100% pure, usable isotope, which does not require enrichment, whereas natural uranium contains only 0.7% fissionable U-235;
* Thorium can not sustain a nuclear chain reaction without priming, so fission stops by default.

Weapons-grade fissionable material (U-233) is harder to retrieve safely and clandestinely from a thorium reactor

Thorium is not actually a “fuel” because it is not fissile and therefore cannot be used to start or sustain a nuclear chain reaction. A fissile material, such as uranium235 (U235) or plutonium239 (which is made in reactors from uranium238), is required to kickstart the reaction. The enriched uranium fuel or plutonium fuel also maintains the chain reaction until enough of the thorium target material has been converted into fissile uranium233 (U 233) to take over much or most of the job. An advantage of thorium is that it absorbs slow neutrons relatively efficiently (compared to uranium238) to produce fissile uranium233.
The use of enriched uranium or plutonium in thorium fuel has proliferation implications. Although U235 is found in nature, it is only 0.7 percent of natural uranium, so the proportion of U235 must be industrially increased to make “enriched uranium” for use in reactors. Highly enriched uranium and separated plutonium are nuclear weapons materials.
In addition, U233 is as effective as plutonium239 for making nuclear bombs. In most proposed thorium fuel cycles, reprocessing is required to separate out the U233 for use in fresh fuel. This means that, like uranium fuel with reprocessing, bombmaking material is separated out, making it vulnerable to theft or diversion. Some proposed thorium fuel cycles even require 20% enriched uranium in order to get the chain reaction started in existing reactors using thorium fuel. It takes 90% enrichment to make weaponsusable
uranium, but very little additional work is needed to move from 20% enrichment to 90% enrichment. Most of the separative work is needed to go from natural uranium, which ahs 0.7% uranium235 to 20% U235.

Thorium produces 10 to 10,000 times less long-lived radioactive waste;

Proponents claim that thorium fuel significantly reduces the volume, weight and longterm radiotoxicity of spent fuel. Using thorium in a nuclear reactor creates radioactive waste that proponents claim would only have to be isolated from the environment for 500 years, as opposed to the irradiated uraniumonly fuel that remains dangerous for hundreds of thousands of years. This claim is wrong. The fission of thorium creates longlived fission products like technetium99 (halflife over 200,000 years). While the mix of fission products is somewhat different than with uranium fuel, the same range of fission products is created. With or without reprocessing, these fission products have to be disposed of in a geologic repository.

Thorium comes out of the ground as a 100% pure, usable isotope, which does not require enrichment, whereas natural uranium contains only 0.7% fissionable U-235

Compared to uranium, thorium fuel cycle is likely to be even more costly. In a oncethrough mode, it will need both uranium enrichment (or plutonium separation) and thorium target rod production. In a breeder configuration, it will need reprocessing, which is costly. In addition, as noted, inhalation of thorium232 produces a higher dose than the same amount of uranium238 (either by radioactivity or by weight). Reprocessed thorium creates even more risks due to the highly radioactive U232 created in the reactor. This makes worker protection more difficult and expensive for a given level of annual dose.

(The article goes into a bit more detail. One does have to keep in mind that PSR is generally quite anti nuclear - but I think these are fairly reasonable counterarguments)

Lastly, no one has actually made a commercial level thorium cycle reactor despite decades of trying. It MIGHT have some advantages and engineering and research efforts should continue, but it's hardly a viable solution as of yet.

Nice "fact sheet" by people who are clearly not experts in the field and obviously have an anti-nuclear agenda. Most importantly though, it is anything but objective; it is highly selective of the "facts", full of half truths and strawmen, and has a clear intent to deceive the reader. While I have little desire to sift through their drivel, I fully expect that they have similar "fact sheets" for many other competing energy sources. What we could use is a real fact sheet for fossil fuels, and especially coal...

Just to start with, anything with a half life of 200,000 years is so stable, that it is only technically "radioactive", and poses no health risk whatsoever, beyond possible issues of toxicity. Any residual radiation remaining after a few hundred years is below the background level; the only reason to point out things like this is to incite fear and induce hysteria.

Otherwise, while some hypothetical straw man reactor in once-through mode might suffer from some imaginary reprocessing problems, real designs such as the Molten Salt Reactor are conveniently ignored. There is no solid fuel to start with, no separation necessary, and the "reprocessing" is basically just removing the reaction products, and can be done online.

The amount of real waste from such reactors is so small, and the timeframes so short, that it is ludicrous to even begin talking about geologic storage. For a comparison of the waste and mining requirements, see this presentation [energyfromthorium.com]. In terms of raw environmental devastation and heath effects, it would also be nice to see a comparison with coal.

Th has very real issues. It is just another fuel cycle and you *must* breed U233 to make it work. It produces similar wastes and the whole 10-1000 times lest waste is only if your compare once through with reprocessing and you get the same results regardless of the fuel (U235 compared to U233). In fact a huge chuck of the "Benefits of Th" is from using a molten salt reactor. You get the same benefits if you use U in a molten salt configuration as well.

I was going to mod this up but decided to respond instead*. The Physicians for Social Responsibility has a tagline of "United States Affiliate of International Physicians for the Prevention of Nuclear War". Which raises serious questions about their credibility.

Sooo..... being against nuclear war means that you suddenly cannot possibly put together a cogent and reasonable analysis of the risks in a nuclear reactor? Why do you think that?

See, the problem with this sort of bullshit commentary is that you can dismiss everything and everyone as being "tainted", and therefore unreliable. Not only does everyone have by definition a certain amount of bias, but anyone can be accused of harboring some secret agenda, without them having any chance at disproving it. This mak

Since a CANDU (Heavy Water) reactor's fuel isn't naturally capable of going critical, couldn't that existing, tried and true design be used instead? We can fuel it with nuclear waste from American reactors, or use raw uranium ore, with no need for centrifuges or other tech that can be used to create nuclear weapons. If the cooling system fails, then you should have the backup of draining the heavy water from the reactor core, thus killing the reaction.

I'm not saying that's the only solution, I'm just saying that a known good solution that's been working for decades is probably better than a new one.

CANDU is banned in the US because it has a small positive void coefficient when initially fueled. Over the life of the fuel it moves into small negative void coefficient - basically the reactor is neutral. Chernobyl had a HUGE positive void coefficient so that was probably a reason why CANDU is banned - another is it would compete with US corps.

But TBH, CANDU reactor was the first reactor designed for safe power generation. The BWR and similar designs are scaled up version of what drives US aircraft carrier

I read a wired article about how using thorium instead of uranium will give you a much safer reactor, and would cause much less damage in the case of a meltdown. Also, thorium nuclear power can't be used to fuel WMD's. In the article, it was saying that its inability to be used as WMD's is why it wasn't developed back in the 50's. Our country wanted to make nukes.
Anyone know anything about this, or am I just crazy?

It's funny, because I've seen a couple U.S. nuclear industry representatives/experts on TV being asked about the disaster, could it happen to our reactors, is nuclear power safe? And they'd hem and haw and talk about designing structures around local conditions. Nothing about technology itself. I'm guessing because they don't want to have to talk about how outdated reactor designs in the U.S. are, and how we didn't keep up in research so they're going to be outdated for quite some time. Especially since

First, the Fukushima Daichi reactor is Generation II, using powered pumps. Long ago now, Generation III plants were designed that use natural convection to circulate the coolant, making this whole entry in Slashdot pretty damned irrelevant.

Second, the U.S. is not behind in research. Quite the contrary. What the U.S. has been behind in, has been public support for nuclear power, and thus financing and funding for nuclear power.

and from what I've read, putting the backup generators in water proof rooms would have solved the problem too. I guess they need to keep a big ass extension cord around next time to bring in outside power when their generators flood. If those generators really did get flooded and taken out the tsunami, the operator should be blamed for the event, not mother nature. IMO

Another promising reactor design is the pebble-bed reactor. Its reaction has a negative temperature coefficient, meaning that the reaction self-moderates if it gets too hot, rather than requiring an external control system to prevent meltdown. This means that if the cooling system were to fail, the reactor would just sit in a mostly-dormant state until cooling was re-established.

If nuclear power plants are used to power cities, why can't they power their own cooling? Seems like keeping the darn thing running would be safer than watching it sit there unpowered and on the verge of blowing up. (Don't get me wrong; I'm sure there's a good reason. I'm just curious.)

You are exactly right. The Fukushima plant actually had steam-powered water pumps that could have kept the core cool during operation. But the reactor was automatically (or procedurally?) SCRAM'd at the first sign of the earthquake, which means that the reactor wasn't putting out close to enough steam to power the pumps.

Seems simple to me: Put some stirling engines with big heatsinks in and out of the reactor vessel to provide continual energy for cooling. With the reactors running at 7% load, you can still siphon lots of power.

It seems like it should be possible to design a closed storage pool that would use depleted fuel rods' decay heat to create circulation through a passive radiator of some sort, delaying or eliminating the need for powered cooling.

If nuclear power plants are used to power cities, why can't they power their own cooling?

They do power their own cooling.

Alas, when you shut the plant down, it stops providing power for its own cooling. Which they did here.

Note that the kneejerk response (earthquake, therefore shutdown the reactor!!!!), was, in this case, absolutely the worst thing that could be done. If they'd left the reactor running but begun a slow shutdown (as opposed to a SCRAM), they'd likely have had enough power to keep things

I'm sorry, but that is one of the most misleading and misinformed sequence of words to get marked up regarding this whole issue.

First off, it should be noted that this reactor was in the middle of what can be considered by the general public as three chronological regimes of reactors:

1. Very unsafe reactors that have little or no passive safeguards (i.e. reactors reminiscent of Chernobyl or Simcity2k's 50 year kaboom)2. Relatively safe reactors that have many passive safeguards (multiple layers of containment, and spill region with unfavorable fission geometry etc.) but that still rely on external containment measures (active cooling in the situation we're discussing now)And finally3. Very safe reactors that have many passive safeguards built in for every foreseeable (keyword, so no need to go thinking up magical exceptions to this category) circumstance (such as the capability to snuff themselves out via high concentrations of neutron absorbing daughters etc). As these reactors were being constructed and developed during a period of nonproliferation and disarmament, you see mixed results as many in operation were also once-off prototypes, but there are many places (Japan, France, Canada, etc.) where standarization and continued development/production means that most of the public fear is about as accurate as the tea party's propaganda regarding Kenyan birth records.

As an aside, it's also a good time to note that nuclear power plants are still nothing more than a fancy way to boil water. I.e. after a few heat exchange processes, the steamy water from these reactions is still used to do what water flowing downhill is used for, to drive a turbine.

Now the important part: Shutting down the reactors was by far the correct thing to do here because cooling was necessary for the daughter isotopes.That is, the stuff we've been cooling all this time is the result of decay from before the plant was shut down.

What does this mean? Now here comes the simple part: It means that if you took the exact same situation, but kept the reactors running critically (i.e. no full insertion of control rods), you'd not only continue to generate heat from the primary fission reaction itself, but ALSO continue to generate more heat from the fission of the daughter products.

So sure, you might have had a few hours, hell maybe a day to generate additional energy before the subsequent tsunami--that managed to wipe out: the national electrical grid, thirteen backup diesel generators; and backup batteries that last for eight hours--is now expected to leave your steam turbine energy generation system completely untouched and functional. (http://www.voximate.com/blog/article/1058/failover-backup-systems-redundant/)And in the very very likely case that it doesn't? Well now you have all that additional heat as well as even more daughter products to take care of.

No manuals will be rewritten, if this shit happens again they'll shut down the plants just like they did this time, only get plugs that fit rather than risking a full blown meltdown while hoping that a damaged powerplant can supply its own cooling somehow.

And of-course, if these defunct cores are replaces with newer designs after this is all over, we'll be in much better shape regardless.

Now the important part: Shutting down the reactors was by far the correct thing to do here because cooling was necessary for the daughter isotopes.
That is, the stuff we've been cooling all this time is the result of decay from before the plant was shut down.

It should perhaps be noted that I'm a former reactor plan operator. I have a clue.

Yes, cooling the daughter isotopes is exactly the issue. You generate fewer of them when you reduce output from commercial levels to self-sustaining levels.

And when you reduce power (but not shutdown completely), the decay products begin to decay down toward the new steady-state level. Which is a LOT less than steady state when you're operating at 90%+.

Every minute that goes by with the reactor operating at a reduced output is another minute you don't have to find an external power source to cool things down. And another minute farther from a core meltdown.

As was, by doing a hard shutdown immediately, the reactor was placed into a position such that the only possible way for a "good" outcome would be for the national electrical grid to stay completely intact during the next few days. There's no way that the battery back-up they had could keep cooling that plant for the next couple days by itself.

Which leaves as your only real option to try to use the reactor's output to maintain cooling while you burn through the decay products for as long as possible. After all, you can always scram the reactor later, if things don't work out.

If nuclear power plants are used to power cities, why can't they power their own cooling? Seems like keeping the darn thing running would be safer than watching it sit there unpowered and on the verge of blowing up. (Don't get me wrong; I'm sure there's a good reason. I'm just curious.)

The reactors were configured to shutdown when a major earthquake hit as a precautionary action, which they did. The reactors would then use power from the grid to continue cooling. Just in case the grid had issues, there were on-site generators (which I've heard were not sitting above ground, but I'm not 100% sure on that one). The tsunami knocked out the power lines to/from the grid and either the generators or the electronics between the generators and the reactor.

Because, in order for the reactor to produce power it needs at least some of its control rods to be removed. Having the control rods removed during an emergency is FAR FAR more dangerous than a loss of cooling. The point of the cooling pumps is to prevent the core from getting so hot that it melts the control rods and the slags down to the bottom of the containment chamber. All modern reactor designs do not need active cooling like these reactors do. They are some of the oldest reactor designs in existence and upgrading such reactors have by put off due to cost and unending legal challenges by environmental groups. It's sad that we could replace our horrendous coal and hydroelectric power grid that does untold damage to the environment, with modern safe reactors within a few decades but can't because "Environmental" groups hold on to this windmill pipe dream... oh wait, they file legal challenges on the windmills to...

That's because the studies aren't sensitive enough and don't include sufficient population. Chernobyl basically affected a few hundred million people all over Europe. Are these studies sensitive enough to pick up small increases in cancer rates, e.g. a dozen additional cases per year in a population of half a billion people? I don't think so.

You're right, they're not sensitive enough. They can't be. The problem is that such levels are well below the noise threshold in background radiation, let alone variations in exposure to other carcinogens. For example, naturally-occurring radon emissions cause more than 20,000 lung cancer deaths a year in the USA.

If you are scared of nuclear fission power generation, you should be terrified of getting out of bed in the morning.

When something goes wrong you have to stop the reaction shutting down the generation. Or the something that goes wrong damages something else along the line similarly stopping the generation. Hey presto, no more power for cooling. You probably could for a lot of situations, but for that one time every goes very wrong, kinda like fukushima, you don't want to have to rely upon it.

It's like asking why my car won't start when the engine is blown. Or why my wounds aren't healing when I'm already dead. The power plants just broke. It's not really an issue of how they're suppose to work at that point but rather the extent of how fault tolerant they are. Like airbags if it were a car etc.

And they do have their own cooling, as well as battery backup for cooling. In the case of many of these failed reactors, the battery backup was in the basement, where it was flooded. If only there was some technology that could have saved the day, like not putting batteries in the basement below sea level. Someday...

A related question is - why can't the decay heat be used to actually produce power? Why can't the steam turbines continue to operate after shutting down the reactor, since it's still producing a lot of heat?

Yeah, that's been bugging me for quite a while now. They have steam-turbines and generators, and a fuckload of steam. What's the problem?

I'd love one of these in the back of my field connected to the grid. A cool 10MW or so is all I need.

These are only the size of a shipping container and are a self contained unit. They would be a great way to bypass the NIMBYism associated with nuclear power plants. They are also much safer. If these can be bought by people with a bit of cash in the attic and installed in the countryside unknown to the neighbours we can all enjoy cheap nucular energy while everyone is blisfully oblivious to the fact that the neighbours little 'storage' container is actually a nucular power plant

These are only the size of a shipping container and are a self contained unit. They would be a great way to bypass the NIMBYism associated with nuclear power plants. They are also much safer. If these can be bought by people with a bit of cash in the attic and installed in the countryside unknown to the neighbours we can all enjoy cheap nucular energy while everyone is blisfully oblivious to the fact that the neighbours little 'storage' container is actually a nucular power plant

It turns out that pebble beds aren't quite so maintenance free. Although the helium used as a coolant doesn't become radioactive, the graphite in the pebbles absorb radioactive metals and spread it around in graphite dust particles. Both the the AVR and HTR reactors in germany had big problems with contamination of the reactors due to this and due to the inability of the pebbles to contain radioactive isotopes.

Also, the pebble bed itself can't be instrumented so it becomes a black box resulting in unexpected hot currents of gas that can be significantly (200+K) warmer than expected. This resulted in maintenance issues in the two reactors in Germany (I don't think there is information on other experimental or production reactors using a pebble bed design). These problems might be surmountable but right now they're pretty big issues.

It's also a great fuel for nuclear reactors. Keep two fast-breeder plants running in slightly different configurations, and you never have nuclear waste to worry about - you can take "waste" from older reactor designs and burn that up.

Non breeder reactors, like every power reactor on the planet, also make plutonium.

For weapons you want only Pu-239 and not much Pu-240 or heavier nuclei which will cause problems in your weapons.

The only thing is that you take the fuel rods out early (uneconomically) if you want to make weapons.

In either case, the critical problem is cracking open the fuel rods and separating the plutonium from the very dangerous (if free) radioactive products. Reprocessing is the critical technology for weapons manufactur

Be it the levees that failed in New Orleans, or the I-35W bridge over the Mississippi, it isn't a lack of innovation that causes any of these disasters. It is in lack of maintenance, and just *caring* in general.

"If it ain't broke, don't fix it."

Well, look where it got us.

I would contest innovation actually. That is how governments waste tax dollars. Stick to time tested simple solutions that multiple contractors can compete for. Innovation is for the private sector.

I'm having trouble finding any details on what makes this TWR reactor safe. They mention that it uses passive liquid metal cooling to ensure safety, but even passive cooling has potential failure modes. They state that relying on the laws of physics makes for a reliable reactor, but the laws of physics that govern diesel generators are well studied, yet they still failed at Fukushima.

From reading about other liquid metal designs, it sounds like natural convection alone is enough to keep the coolant flowing,

"the two biggest advantages of the fast reactor design is that it requires no spent fuel pools and uses cooling systems that require no power to function"

Let's translate what this means. The core of the reactor will be VERY radioactive as it will have decay products from many more gigawatt hours---yes it will transmute quite a bit of these but do not underestimate just how hot it will be.

The cooling systems use molten sodium. It has the wee problem that it is explosive in contact with water. Say from a flood. Or if the building catches on fire. (and it's probably quite radioactive in itself simply from activation from the neutron flux). Or suppose there's a leak in the roof and it rains.

And it's right next to an extremely radioactive core. And if the explosion results in something cracking open......

One huge problem at Fukushima reactors was the unappreciated dangers of flooding, combined with the hydrogen explosions. These explosions damaged other important machinery and structures---you get a 'blunder chain reaction'.

The cooling systems use molten sodium. It has the wee problem that it is explosive in contact with water.

There was a serious sodium coolant leak at the Japanese Monju reactor [wikipedia.org] in 1995. It got so hot that steel structures in the room started to melt. You can imagine how such a leak could result in the destruction of other critical safety systems.

The more I learn about nuclear reactors, the more I learn of the potentially catastrophic accidents that have occurred along with a catalogue of lies, safety report falsifications and cover-ups. Nuclear does not seem to be a very safe way forward.

Great idea. Let's build a huge potential bomb by placing a metal that reacts violently with pretty much anything else next to the substance that it reacts most violently with.

and if there's a reactor problem the barrier dividing the two is lowered resulting in radioactive NaCl being created?

The reaction between chlorine and sodium is hugely exothermic. What you propose basically amounts to blowing the reactor and its contents sky-high.

Also, you don't want chlorine anywhere near neutron radiation, since the Cl-36 created that way has a half-life of a few hundred thousand years. Short enough to make it a radiation hazard, and yet long enough to make disposal quite difficult.

Once again, the folks at Freakonomics suggest that the solution to a problems is some new technology.

But they just won't go far enough and say "What about a "new technology" for energy that is not based upon another scarce resource?"

It's surprising to me that this "Freakonomics" movement, which prides itself on "thinking outside the box" is such a prolific purveyor of short-sighted conventional wisdom.

If they were just engaging in thought experiments it might be benign, but you've got people out there who take what these economists say as gospel. Instead of attacking the pseudo-science of Economics as the drivel that it is, they are simply supplanting it with even more banal pronouncements.

I think it's time to say to all of the post WWI economists, including the Freakshop, that you've done enough damage and put them on the shelf next to astrology and phrenology where they belong.

Which reminds me, that the Nosferatu of Economists, Alan Greenspan, showed his ugly face in public again [nytimes.com] in the past few days, demonstrating again that when you are among the economic or political elite, no matter how badly you fuck up everything that can be fucked up, no matter how much pain you cause to fellow humans, no matter how often you are catastrophically wrong, again and again, once the Media Elite believe you are one of the "Wise Old Men" you never ever have to feel the least bit of shame or remorse and there will always be a seat for you at the tables of the Sunday Morning News Shows. (See McCain, John and Lieberman, Joe for further examples).

As long as I'm at it, did anyone else notice that Colin Powell's son, who was the head of the FCC under George W Bush has now taken a job at the head of the largest and richest lobbying firms representing the Cable Television Industry? What are the chances that he was auditioning for this job when he was making cable TV policy at the FCC? These fuckers will destroy our world, utterly.

As long as we have Jimmy Carter around, I'm not worried bout no meltdowns.

THORIUM is the answer. You just aren't asking the right question.

"On Dec. 12, 1952, the NRX reactor at Atomic Energy of Canada’s Chalk River Laboratories suffered a partial meltdown. There was an explosion and millions of litres of radioactive water ended up in the reactor building’s basement. The crucial reactor’s core was no longer usable.
With the Cold War then in full swing, and considering this was one of the first nuclear accidents in the West, the Americans took a great interest in the cleanup.
Mr. Carter was a young U.S. Navy officer based in Schenectady, New York, who was working closely with Admiral Hyman Rickover on the nuclear propulsion system for the Sea Wolf submarine. He was quickly ordered to Chalk River, joining other Canadian and American service personnel.
“I was in charge of building the second atomic submarine and that is why I went up there,” said Mr. Carter. “There were 23 of us and I was in charge. I took my crew up there on the train.”
Once his turn came, Mr. Carter, wearing white protective clothes that probably, by today’s standards, provided little if any protection from the surging radiation levels, was lowered into the reactor core for less than 90 seconds."

Good Lord. This looks like a total scam. This is all funded by a known patent troll. It appears to be some sort of viral marketing campaign to drum up customers, i.e. moronic investors willing to part with huge sums of money they will never see again. And now we're all part of it, they'll point at Slashdot and say, "Look! Nerds are talking about it. Smart people. See them talking about it? Now give me some money." I feel dirty now.

Or we could put the panels in the desert and let the people live where ever they like. I know crazy idea.

Sure nukes have a place, but at this point they are more heavily subsidized than any other power generation method. I say that because cleanup costs always come from the tax payer. Solar thermal plants in our deserts and Wind where that fits can be a large part of our power needs. Nukes will still be needed, but unless something can be done about their high costs, coal will sadly stay in use.

Nukes will still be needed, but unless something can be done about their high costs, coal will sadly stay in use.

Nukes only seem expensive because you're comparing them to coal, which has massive external costs not accounted for. Compare nukes to other massively-scalable generating technology that emits low CO2 (e.g. what, again?) and they start to look pretty good.

Engineering get better through failure. This is why cars, airplanes, household electricity, etc. are safe. Engineers do the best they can with the existing experience base, and then see what happens. Over a long enough period of time, and enough failures, safe and cost effective results can be produced.

How many Level 5 nuclear events will it take to achieve an acceptable level of safety? The only way to answer this question is to keep on building rea

Wouldn't it be better to not build nuclear plants in earthquake prone areas?

Good idea. I'll let you go tell the Japanese that they have to dismantle their entire economy and cut their population by 25% because they're not allowed to have electricity any more.

34.5% of Japan's energy comes from nuclear reactors. 21st century Japan would be an entirely different country without nuclear power. Or perhaps you think they should be burning dinosaurs for their power?